Compass needle

This highly conjugated molecule was stabilised with nitroxyl biradical side chains. The resulting material had sufficient ferromagnetism that a usable compass needle could be made from it. Despite the success of this demonstration, organic ferromagnetism remains a curiosity. Such polymers are not likely to replace conventional ferromagnetic metals in any application within the foreseeable future. 

Owing to the shape of the earth s magnetic field, a compass needle points downward only in the Northern Hemisphere. In the Southern Hemisphere, the field s curvature causes the needle to point north and upward. Here, the south end of the needle points downward. As a result, the magnetic sense of New Zealand bacteria works in the opposite direction. They too should remain near... 

Because of its hard brittle nature, the metal osmium has few uses. However, the powdered form can be sintered under high pressure and temperatures to form some useful products, despite its toxicity and malodor. Its main use is as an alloy to manufacture devices that resist wear and stand up to constant use. As an alloy, osmium loses both its foul odor and toxicity. Some of these products are ballpoint and fountain pen tips, needles for record players, and pivot points for compass needles. Osmium alloys are also used for contact points on special switches and other devices that require reduced frictional wear. 

Now consider C12CH—CH=0, in which the protons are in close proximity to one another, three bonds apart. Each of these protons has a magnetic field and two possible magnetic states that correspond to a compass needle pointing either north or south (see Figure 9-21). The interactions between a north-... 

Static Objects deflecting compass needles bending metal keys making stopped watches run. 

Figure 5. Physical origin of magnetic anisotropy (a) compass-needle analogy of shape anisotropy and (b-c) magnetocrystalline anisotropy. In (b) and (c), the anisotropy energy is given by the electrostatic repulsion between the tripositive rare-earth ions and the negative crystal-field charges.

Let us return to the compass for a moment. We have already seen that if we could switch off the earth s magnetic field it would be easy to turn the compass needle round. When it is back on we need to push the needle (do work) to displace it from north. If we turned up the earth s magnetic field still more, it would be e ven harder to displace the compass needle. Exactly how hard it is to turn the compass needle depends on how strong the earth s magnetic field is and also on how well our needle is magnetized—if it is only weakly magnetized, it is much easier to turn it round and, if it isn t magnetized at all, it is free to rotate. 

The aim hae is to take a microscopic view of an ion inside a solvent. The central consideration is that ions orient dipoles. The spherically symmetrical electric field of the ion may tear water dipoles out of the water lattice and make them point (like compass needles oriented toward a magnetic pole) with the appropriate charged end toward the central ion. Hence, viewing the ion as a point charge and the solvent molecules as electric dipoles, one obtains apicture of ion-dipole forces as the principal source of ion-solvent interactions. 

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